Actor and comedian Bill Cosby reacts after a judge declared a mistrial in his sexual assault trial at the Montgomery County Courthouse in Norristown
Thomson Reuters

The sexual assault trial of 79-year-old comedian Bill Cosby — who was commonly known as "America's Dad" — was declared a mistrial on Saturday after jurors failed to reach a verdict after six days of testimony and closing arguments.

Cosby stands charged with three counts of aggravated sexual assault after he was accused of giving drugs to and molesting former Temple University employee Andrea Constand at his home outside Philadelphia back in 2004. Constand first filed a civil claim against Cosby in 2005. In total, Cosby has been accused of sexual misconduct by nearly 60 women.

Despite 52 hours of deliberation, jurors in the Cosby trial told Judge Steven O'Neill on Saturday that they were "hopelessly deadlocked" and could not reach a unanimous verdict. O'Neill then declared a mistrial.

What is a mistrial?

A mistrial is a trial that has not reached its normal conclusion, has no legal consequences, and is considered invalid. Though numerous factors can result in a mistrial, including lack of jurisdiction and incorrect jury selection, a hung jury — a jury that's unable to unanimously come to a verdict — is the most common reason.

The unanimous verdict has long been considered a "defining feature" of jury trials, according to Jeffrey Abramson in "We, the Jury," dating back more than 600 years in England. Such was the case in the US until 1972, when the Supreme Court ruled in Apodaca v. Oregon that a state jury could convict a defendant by a less-than-unanimous margin, though a federal jury must still agree unanimously.

Today, however, all states but Louisiana and Oregon require a unanimous verdict for criminal trials. That includes Pennsylvania.

After arriving at an impasse on Thursday, the jurors in Bill Cosby's sexual assault trial asked the judge to clarify the definition of "reasonable doubt" on Friday.

Benedict Morelli, a prominent trial attorney who represented Tracy Morgan in the case against Wal-Mart, told Business Insider on Friday that the fact that the jurors asked the judge to clarify the concept of reasonable doubt meant it was likely one or two jurors were holding out against finding Cosby guilty rather than the other way around.

What happens in the event of a mistrial?

When a mistrial is declared, it is up to the government to decide whether it wants to drop the prosecution or attempt a retrial.

Gloria Allred, who represents a number of Cosby accusers, said after the mistrial was declared that "We can never underestimate the blinding power of celebrity." One of Allred's clients, Kelly Johnson, appeared as a witness for the prosecution in Cosby's trial.

"I hope that the prosecution will try this case again and that the next time the court will permit more priority bad act witnesses to testify as the prosecution had requested for this trial," Allred said. "For the trial that just ended, the court only allowed one such prior bad act witness to testify. And that was my client, Kelly Johnson, rather than the 13 such witnesses which the prosecution wanted to call."